High-speed microtome



June 23, 1953 R. G. PICARD ETAL 2,642,774

HIGH-SPEED MIcRoTouE Filed oct. 29, 1947 :inventors ROBERTS. PICARD L Tm-m H. RSNEH 1' y dttomeg A in mounting and adjusting the Patented June 23, Y 1953 UNiiTED STATES PATENT ori-ICE HIGH-'SPEED MICRGTOME Robert G. Picard and `lohn H. Reisner, Collingswood,.N. J., assignors to Radio Corporation of America, a corporation .of .Delaware Application Getober 29, 1947, Serial *No. 782,886

(o1. .ss-.40)

1 Claim. l

invention relates @to Ath'e .art of cutting, sorting and collecting .pellicle-like -sections of a Aspecimen for :microscopic examination.

It may `be said, generally, that .sections yof .a specimen thin venough for use in .a light .microscope-are usually too .thick-for Ause in an .electron microscope. This l.is so because of the .relatively poor penetrating power of even vthe highest ve- Vflocity electrons. However, the .superior resolving power of the :electron microscope has .cre-

ated .a demand for thinner and yet thinner 4specinien-sections.and has led to many improvements Tin fthe art of cutting such sections. In fact, present-day high-speed m-icrotomes (such, tor example, as .the .ones described by Fullam .and 'Gessler "in vThe Review :of :Scientific Instruments vol. 17., No. 1, January, 194.6,1pp- 23-35.) .are said to be .capable of cutting .specimen materials into .slices less than one micron thick.

In the operation of present day high-speed microtomes the thin specimen-sections are cut and pile-up .at the rate of many hundred per 4second and, because of the extreme thinness of lsuch sections, it .is very difficult to extract discrete Whole specimens from the pile. 'Furthermore, in spite of the use of extreme care specimen holder 4with respect to Vthe cutting blade it is impossible to Aachieve 'perfect uniformity in the shape Land dimensions of the specimensections. Thus, some sections `may be curled-up by the action of the blade, er may become dis- 'torted 'by impact with the pile of previously -cut sections. Such lack of uniformity in they physical characteristics l'of 4the sections, yplus the nat- .ural tendency of such thin films Lto adhere -to -each other, further complicates the problem Aof :separating the pile into its individual Aelements and Jof selecting -the usable from the non-usable elements.

Accordingly, the principal object ofthe present invention 'is to obviate `the foregoing and other Iless apparent objections to present day methods o'f cutting and selecting specimen sections 'for microscopic examination.

Another and related object of the'present invention is to provide an improved 'high-speed microtome, .and one capable not only of cutting .specimen-sections .thin enough for use in an electron microscope, but one which shall directthe rsaid sections into separate paths determined by ltheir physical characteristics yand shall sepamately collect fthe individual Aonesof Ythe `fspecinfxen :sections 'in :each of said paths.

. The invention will .be rdescribed in connection with l'the `accompanying drawing wherein:

Fig. 1 is a sectional elevation of a high-speed microtome constructed and operated in accord- '.ance with the `4principle `of the present invention; Fig. 2 is an fenlargedr front view, partly in sec- ;tion, of the cutting blade of the device of Fig. l; Fig. y3 is .a ,section ,ofr the blade taken on the :line ,III- III of Fig. 2,; Fig. ,4 isa .plan view of the blade.: liir..5r is an enlarged elevational view 4partly :in section of the specimen holder shown .in ,.1; ,and Fig. ,6 is a fragmentary View of .the microtome showing an alternative form of `.collecting surface for the Yspecimen sections.

.,Microtomes constructed in accordance with the principle `of the ,present invention consist, essentially, oflavcutting blade l, aspecimen holder 2 ,foraspecimen -,(I,5.Fig. 5) and a movable surface 3 (Fig. 1, 3d Fig. 6) upon which the dis- -cretely cut specimen sections (indicated by the ibroken lines a, bFig. l, a. b, c Fig. 6) are sepa- :.rately collected. These .essential parts I, 2 and 3 areshown mounted for relative movement, in .ainannerlater described, in an evacuable cham- I ber-:4v whichwill be .understood to be maintained `atra.vacuum of the-order microns or less.

agreement with the generally accepted Iltheory that the .higher the cutting speed 'the thinner the cut, the microtome shown in the .drawing isconstructed to operate at the 'high- .estpracticalspeed (ordinarily in the range of from 5,00 to 1200 revolutions per second), the upperspeed `limit .being `determined by the burst- ;ing ,point of the rotor. To thisend, the blade ,l is mountedupon aholder 5 which projects ,from the ,periphery of a solid metal rotor '6 (say, four inches in diameter) having a shaft 1 which extends through a rubber or other suitable vacuum-tight 'bearing' 8 in the lid of the chamber v4.. Thus, at 500 revolutions per second, the `flywheel will lhave a peripheral klinear velocity -of .'10'00 inches per second. The blade YI will, o1'

course, 'have a Alinear velocit-y somewhat in excess of `1'000 `inches per second, depending vupon vhow far it extends beyond the periphery vof the flywheel. lThe bearing 9 4for the lower end 0f the s'hafft 11 is contained within the chamber 4.

`This A.shaft l terminates, `exterior of the chamber 4, .in a Pelton Wheel `,Ill which is arranged .to be :driven by compressed air applied to theflutes Il, of the rvWheel throughnozzles I.2

:In order to v`minimize drag in the supporting ,bearing, :the rotor 6 and its rvshaft kl are mounted to permit.4 of slight A,axial movement. .Such ,movementis provided aby an auxiliary source of air I3 which operates to lift the wheel Ill (say, one or two thousandths of an inch) so that there is no load or thrust on the ends of the shaft 1. The shaft "I is relatively thin (say, 115" diameter) so that it can flex, making the rotor substantially free to seek its own center of rotation. The unbalance which might be occasioned by the presence of the blade I is compensated by small weights I4 suitably distributed on the periphery of the rotor.

As shown more clearly in Figs. 2 and 3 the holder for the blade I may comprise simply a short threaded rod 5, which is screwed into a complementarily threaded hole Ss in the periphery of the rotor, and having a bifurcated free-end containing two screws 5s which serve to clamp the blade I by its neck In (Fig. 4) in a position to be brought into cutting relation with respect to the specimen I5 in the specimen holder 2. The cutting angle may be adjusted simply by turning the blade holder 5 in its threaded seat 6s and clamping it by means of a set screw Gt.

As shown in Fig. 5, the specimen I5 is preferably embedded in a thermoplastic or other hardened plastic material I6 contained in a small cup-shape receptacle I1 which is secured by screws I8 on the upper end of the vertically movable holder 2. Referring again to Fig. 1; this rod-like holder 2 extends through a vacuum tight bearing I9 to the exterior of the chamber and is provided adjacent to its outer end with a micrometer screw 2m for moving the rod, and hence the specimen I5 thereon with respect to the plane of movement of the blade I. This movement is preferably continuous and may be imparted t0 the holder by means of a motor driven belt 20 wrapped about a pulley 2I on the end of the threaded rod 2.

As previously set forth, in the high-speed microtomes of the prior art the cut sections of the specimen are deposited and pile-up upon a stationary collecting surface and it is exceedingly difficult to extract discrete whole specimens from the pile. lThis difculty is obviated, in accordance with the present invention, by the provision of a movable collecting surface 3 Fig. 1 (3d, Fig. 6) upon which the cut sections areseparately deposited.

The speed at which is driven should preferably permit the discrete sections to be deposited upon separate elemental areas of said surface without any overlapping of the sections. For example, in one embodiment of the invention wherein the sections (in this case sections of carnauba wax) were cut at the rate of 500 per second, and were about 0.1 of a micron thick and 1 millimeter the collecting surface 3 diameter, the collecting surface (in this case a disc) was rotated at a rate of only 0.5 meter per second at the point of contact, without any overlapping of the successively deposited sections. Faster speeds were, of course, also satisfactory. A. disc-shape collecting surface is ordinarily to be preferred to a drum, cone, belt or sphere because the plane surface of a disc lends itself more readily to a preliminary inspection of the sections under a, light microscope. The surface of the collector may be coated with oil, or with an organic film (e. g. collodion) to cause the specimen sections to adhere more readily thereto. If desired the collector may comprise a fine-wire screen (say, 200 mesh) which may subsequently be cut (with a punch) be great enough to 4 about the individual specimen sections and the separate pieces of the screen mounted directly in the specimen holder of the electron microscope.

The direction of movement of the collecting surface 3 should preferably be the same as that of the rotor 6, as this reduces the relative velocity of the cut sections with respect to the said surface. By thus reducing the relative velocity of the arriving sections with respect to the collector 3 the possibility of damaging the said sections by the force of their impact upon the collector is materially reduced. When, as in the illustrated embodiment of the invention, the cut sections of the specimen are projected upwardly their velocities are still further reduced in overcoming the force of gravity. However, it is apparent that the principle of the moving collector surface may be applied irrespective of the direction (e. g. up or down or sideways) in which the cut sections are projected.

When, as contemplated, the forces applied to the specimen I5 by the blade I are of the proper direction and intensity to project the severed sections a substantial distance (say 2 or 3 inches) into space the trajectories of said sections are not always the same but will differ as determined by the physical characteristics of the said sections. Thus, curled-up pieces, and pieces of different mass will be deposited different distances from the edge of the collecting surface. By way of example, if as indicated by the dotted lines a and b of Fig. 1, the cut sections comprise only large and small pieces, the larger pieces a will not travel as far as the smaller pieces b and will be deposited nearer the center of the disc 3. As indicated by the several dotted lines a, b and c in Fig. 5 the cut sections may be of several sizes and hence be deposited in several rings or rows. However, since the section in all of the rows are separated one from another (by reason of the prescribed movement of the collecting surface) the selection of a given section or row of sections for microscopic examination is greatly facilitated.

It will now be apparent that the present invention provides an improved method of, and apparatus for, cutting and sorting and collecting extremely thin sections of a specimen for microscopic examination.

What is claimed is:

In a high speed microtome, means for simultaneously subjecting a specimen to a cutting force of sufficient intensity to sever discrete sections from said specimen and to a projecting force sufficient to project said severed sections into space along separate paths determined by the mass of said sections; said means including a rotatable member, a severing blade secured to the periphery of said rotatable member, and means for driving said blade at a linear velocity of at least 1000 inches per second; a collecting surface for collecting said severed and projected sections, said collecting surface being rotatably mounted in a position to intercept the separate paths of projection of said sections, means for rotating said collecting surface in a direction constituting substantially a continuation of the projection path of said sections and at a velocity determined by the velocity of said rotatable member whereby said specimens will be separately collected on said collecting surface; a vacuum tight chamber, said specimen, said blade, and said collecting surface being mounted within said 5 chamber; and means for evacuating said Number chamber. 1,825,421 ROBERT G. PICARD. 2,001,512 JOHN H. REISNER. 2,162,122 2,215,535 References Cited in the le of this patent 2,239,665 UNITED STATES PATENTS fggg Number Name Date 21473:'753 325,722 Bausch Sept. 8, 1885 10 2,182,853 873,059 Lebrun Dec. 10, 1907` 1,728,843 Trunz Sept. 17, 1929 1,747,461 Vaughan Feb. 18, 1930 Number 1,797,694 Ott Mar. 24, 1931 402,888

Name f -Date Roesch Sept. 29, 1931 Walter May 14, 1935 Resch June 13, 1939 Urschel et a1 Sept. 24, 1940 Straeten Apr'. 22, 1941 Walter May 5, 1942 Urschel et a1. Feb. 24, 1948 Johnson June 21, 1949 Ladd Sept. 27, 1949 FOREIGN PATENTS Country Date Germany Sept. 19, 1924 

